NESTING HABITAT SELECTION OF LOGGERHEAD SHRIKES

ON THE BUTTE VALLEY NATIONAL GRASSLANDS OF

NORTHERN CALIFORNIA


Nathan E. McNett
School of Science and Natural Resources
Lake Superior State University
Sault Ste. Marie, MI 49783

	Abstract.  Loggerhead shrike (Lanius ludovicianus) populations have been on the decline
over much oftheir range. They are listed as a species of special concern in California. Surveys
were conduced for nesting loggerhead shrikes ftom mid-May to early August on the Butte Valley
National Grasslands north of Macdoel, California. Seven shrike territories were located.
Vegetation sampling was conducted at each of the territories and their locations were recorded
with the use of a GPS receiver. Five habitat attributes were evaluated from the vegetation data.
These were: the percent cover of trees, shrubs, grasses & forbs, and bare ground, and the mean
height of shrubs. The locations of shrike territories were overlaid onto a vegetation map using
GIS utility. Shrikes were found to be associated with edges where larger shrubs or trees bordered
shorter shrubs and grasses. The majority of territories were located in an area ofthe grassland
that experiences ponding in the early spring. A Spearman's rank test and a principle components
analysis was performed on the habitat data. The amount of ground cover in the form of grasses
and forbs was found to be the most important factor in determining the presence of shrike
territories with an R-value of .73 and a p-value of .0008. The principle components analysis
reinforced this finding. Shrike territories had a higher percent cover of grasses and forbs and a
lower percentage ofbare ground than areas without shrikes.





Selected References

Hines, J., and J.R. Sauer. 1994. Loggerhead shrike Lanis ludovicianus sur annual indices:
	[on-line] . Available: http ://www. im. nbs.govlbbs/htmgr/h622Ossur. html.

Poole, L.D. 1 992. Reproductive success and nesting habitat of loggerhead shrikes in
	shrubsteppe communities. M. S. Thesis, Oregon State Univ., Corvallis.